Efficient flowering in plants is important, particularly when the intended product is the flower or the seed produced therefrom. One aspect of this is the timing of flowering: advancing or retarding the onset of flowering can be useful to farmers and seed producers. An understanding of the genetic mechanisms which influence flowering provides a means for altering the flowering characteristics of the target plant. Species for which flowering is important to crop production are numerous, all crops which are grown from seed, with important examples being the cereals, rice and maize, probably the most agronomically important in warmer climatic zones, and wheat, barley, oats and rye in more temperate climates. Important seed products are oil seed rape and canola, sugar beet, maize, sunflower, soybean and sorghum. Many crops which are harvested for their roots or leaves are, of course, grown annually from seed and the production of seed of any kind is very dependent upon the ability of the plant to flower, to be pollinated and to set seed. Delaying flowering is important in increasing the yield of plants from which the roots or leaves are harvested. In horticulture, control of the timing of flowering is important. Horticultural plants whose flowering may be controlled include lettuce, endive, spinach and vegetable brassicas including cabbage, broccoli and cauliflower, and carnations and geraniums.
Arabidopsis thaliana is a facultative long day plant, flowering early under long days and late under short days. Because it has a small, well-characterized genome, is relatively easily transformed and regenerated and has a rapid growing cycle, Arabidopsis is an ideal model plant in which to study flowering and its control.
We have discovered that one of the genes required for this response to photoperiod is the Late Elongated Hypocotyl or LHY gene. We have found that plants carrying dominant gain of function mutations of the LHY gene flower later than their wild-types under long days but earlier than their wild-types under short days. We have now cloned and sequenced the LHY gene, which is provided herein, and demonstrated that the mutation causes the gene to be transcribed at higher levels than the wild-type gene. This suggests that increased expression of LHY delays flowering under long days.